Recently in wide use are image projection apparatuses including highly efficient and low cost image projection apparatuses using a reflection type display element such as a Digital Micro-mirror Device (DMD) (Texas Instrument Co., trademark) or a reflection type liquid crystal light bulb, or a transmission type display element such as a transmission type liquid crystal light bulb in television machines for household use for BS digital broadcasting use, home theater application, etc., especially rear projection type image projection apparatuses wherein an image is projected from the rear side of the screen.
Optical systems for image projection have shown marked progress in production of smaller size and higher performance, and have been virtually equalized in image quality and in other performances as compared with expensive panel type television machines.
Image projection apparatuses using the reflection type display element are disclosed, for example, in Japanese Unexamined Patent Publication No. 2003-114479 (JP2003-114479 A) and Japanese Unexamined Patent Publication No. 2003-177320 (JP2003-177320 A). The latter publication also discloses an image projection apparatus using a transmission type display element.
These image projection apparatuses have, in principle, a lighting optical system leading light from a light source for lighting the reflection type display element or the transmission type display element, and a projecting optical system for projecting light reflected from the reflection type display element and containing image information.
However, as the image projection apparatuses have been recognized as television machines and have spread in the market, improved apparatuses have been demanded in view of compacting the image projection apparatus and in view of improving the appearance thereof. For example, in the case of image projection apparatuses having the lighting optical system and the image projecting optical system arranged in a lower portion of the apparatus, such image projection apparatuses have been demanded that a so-called underjaw portion or a so-called skirt portion (hereinafter the portion may be referred to as “screen-underlying portion”) following a screen lower portion is removed when the image projection apparatus is seen from the front side thereof, or the height of the screen-underlying portion, in other words, the length of the screen-underlying portion as measured from the screen (hereinafter the portion may be referred to as “length of screen-underlying portion”) is as short as possible.
Generally speaking, there is now a demand for apparatuses in which a portion following the screen (hereinafter the portion may be referred to as “screen-continuing portion”) corresponding to the area wherein the lighting optical system and the projecting optical system are arranged is as short as possible.
In conventional image projection apparatuses, wherein the lighting optical system and the like are arranged in a lower portion of the image projection apparatus when seen from the front side of the image projection apparatus, the whole or greater part of the lighting optical system is located at substantially the same height or position as an optical axis of projection light coming from the display element and incident into the projecting optical system, or arranged below the optical axis of the projection light so that the length of screen-underlying portion is correspondingly longer. Especially the light source provided in respect of the lighting optical system has a reflector (light reflecting member) with a large paraboloid shape for leading the light to the lighting optical system. This enlarges the length of screen-underlying portion, as coupled with such arrangement of the lighting optical system.
Aforementioned Japanese Unexamined Patent Publication No. 2003-114479 also discloses an image projection apparatus in which the projecting optical system is a so-called L-type image projecting optical system wherein the incident light is emitted as bent, the light source is arranged as raised, and the light source optical axis is greatly inclined from a horizontal plane to shorten the length of screen-underlying portion. However, the extent of raised arrangement of the light source is limited, and minimization of the screen-underlying portion is restricted in view of a light source reflector (light reflection member) which is actually large.